In their weekly email newletter to Direct Market retailers, DC Comics released the cover to issue #4 of its in-house promotional magazine DC Nation, and on the new image the publisher is promising the death of "one" of six characters - Harley Quinn, Cyborg, Booster Gold, Red Robin, Arsenal or Kyle Rayner.
Hitting stores September 5, the 21 days means the promised death will occur on September 26. The likely comic book the date is referring to is of course Tom King and Clay Mann's Heroes in Crisis #1, due in stores on Sept. 26 and featuring a mass shooting resulting in the deaths of multiple heroes that drives the storyline about a superhero crisis center called the Sanctuary.
Booster Gold and Harley Quinn have long been identified as suspects in the murders, so they can likely safely be eliminated. Red Robin recently spent months imprisoned by Mr. Oz (and thought to be dead by Batman) which would make his death probably unlikely.
Arsenal was just revealed to possibly be returning as a cast member of a revamped Red Hood and the Outlaws ... so there's that.
While still far from safe since multiple hero deaths are apparently coming, fans of Wally West will probably breathe a little easier for a few weeks. Wally was just recently sent to the Sanctuary in The Flash #51, and epilogue to the "Flash War" story arc. DC teased a possible Wally death last month during the San Diego Comic-Con, but it looks as if he may be safe ... for now.